The present invention relates to a method and apparatus for receiving discrete parts traveling at a speed and applying the parts to a web or other carrier traveling at a different speed.
Disposable absorbent articles, such as disposable diapers, generally have been manufactured by a process where discrete parts or components of different materials, such as leg elastic, waist elastic, tapes and other fasteners have been applied to a continuously moving carrier web. Often, the speed at which the parts are fed into the process is not the same as the speed of the carrier web itself. Thus, the speed of the parts must be changed to match the speed of the carrier web to properly apply the parts without adversely affecting the process or the finished product.
Similarly, labels are typically placed onto articles when the speed at which the labels are fed into the process is not the same as the speed of the article to be labeled. Thus, the speed of the labels must be changed to match the speed of the carrier web to properly apply the parts without adversely affecting the process or the finished product.
Several different conventional methods for changing the speed of a part or component of material such that it can be applied to a continuously moving carrier web have been known to those skilled in the art.
For example, one method has been known as the slip cut or cut and slip method. A web of material, which is traveling at a slower speed than the carrier web, is fed into a knife and anvil roll having a surface speed equal to speed of the carrier web. The material slips against the surface of the anvil roll until the knife cuts it into discrete pieces. The purpose of the slip is to ensure the correct amount of material is metered into the system at the desired tension prior to cutting. As the material is cut into the discrete parts, vacuum in the anvil roll is activated to hold the discrete part on the anvil without slipping, so that the discrete part is accelerated to the speed of the anvil roll. The anvil roll then carries the part to the point where the vacuum is released and the parts are applied to the carrier web while both the parts and the carrier web are traveling at the same speed. This method has the main drawback that the coefficient of friction between the material to be cut and the anvil roll must be low enough such that, in conjunction with the holding force keeping the materials in contact, the total tension generated in the material to be cut is not great enough to generate significant elongation in the material to be cut. This elongation, if it occurs, can contribute to high variability in the final cut length and placement of the discrete part on the carrier web.
Another method has used festoons to reduce the speed of the carrier web to match the speed of the discrete parts of material to be applied to the web. An example of this method is described in U.S. Pat. No. 5,693,165 issued to Schmitz. The carrier web is temporarily slowed down to the speed of the parts with the excess portion of the carrier web gathering in festoons. The parts of material are then applied to the carrier web while both the parts and the web are traveling at the same speed. The festoons are then released allowing the moving web to return to its original speed. This method has two main drawbacks. First, the carrier web must be festooned and then released; this may damage or otherwise change the properties of the carrier web. Second, the storage system requires a large amount of space in typical disposables production systems because there is a direct relationship between line speed and storage space needed.
Another method has utilized a cam actuated follower arm. The cam actuated follower comprises a cam follower at one end of the arm and a holding plate at the other end of the arm. The cam follower remains in contact with a fixed cam which is mounted concentric with the instantaneous center of rotation of the holding plate. As the holding plate rotates, its radial distance from the center of rotation is increased and decreased to change the surface speed of the holding plate. The discrete parts of material are placed on the holding plate when it is at its smallest radius so that the speeds match. The plate then extends radially enough during the rotation to match the speed of the plate to the speed of the carrier web. At this point the discrete parts are transferred to the carrier web. This method has two main drawbacks. First, the plate is designed to match the curvature of one radius, not both. This means that either the pick-up of the discrete part or the transfer of the discrete part, or both, will occur across a gap for some part of the transfer. This can lead to a loss of control of the discrete part, which impacts handling of parts under tension, such as leg elastics. Second, to achieve the desired change in speed, the mechanical elements typically used, such as cams or linkages, become fairly large to stay within acceptable design limits for accelerations and rise angles. This size leads to increased cost and reduced flexibility, as the unit must be redesigned for each application.
Another method has utilized noncircular gears to change the speed of a transferring device. The means rotates at a constant radius, but the rotational velocity is varied between a minimum and a maximum to pick up the discrete part at its speed and place the part on the carrier web at its speed. This eliminates the size issues and speed or gap mismatch issues, but relies on mechanical means to achieve the change in rotational velocity. The drawback of this is that new transmission parts (gears or other means) are required each time a change in product design occurs that changes placement pitch length, discrete part length, or other key factors. This can be expensive and time-consuming to change. An example of this method is described in U.S. Pat. No. 6,022,443 issued to Rajala and Makovec.
In response to the discussed difficulties and problems encountered in the prior art, a new method and apparatus for receiving discrete parts traveling at a speed, changing the speed of the parts to match the speed of a carrier web or body, and applying the parts to the carrier has been discovered.
In one aspect, the present invention concerns an apparatus for receiving discrete parts traveling at a first speed and applying the parts to a carrier traveling at a second speed. The apparatus comprises at least two rotatable transferring devices and an independent driving mechanism for each transferring device. Each rotatable transferring device comprises at least one shell segment configured to move along an orbital path through a receiving zone where the parts are received and an application zone where the parts are applied to the carrier. The carrier might comprise a continuous moving substrate web or might be another apparatus such as a roll or drum. The driving mechanism utilizes a programmable motor such as a servo motor to transmit rotational energy to the rotatable transferring device. The driving mechanism may transmit rotational energy to the rotatable transferring device through a direct connection or a transmission interposed therebetween. The transmission may include gear to gear contact or gearboxes.
As compared to conventional methods, such as the cut and slip method described above, for changing the speed of a discrete part so that it can be applied to a carrier, utilizing a programmable motor provides the ability to obtain greater changes in speed, to maintain constant speeds for a fixed duration, and to simplify the set-up process when changing from one product to another. Thus, the use of programmable motors can provide a more precise control of the length and placement of the part onto the carrier while offering great flexibility in the type of parts that are to be made.